This paper presents the results of the geological and geomorphological investigation carried out during the first level seismic microzonation project in the Isernia Province territory. The study area falls in one of the most seismically active areas of the Apennine chain and it has been struck, in historical times, by destructive earthquakes that caused several causalities and diffuse damages to the buildings. The analysis points out the occurrence of geological features that can determine possible site amplification phenomena related to areas with extensive outcrops of thick continental deposits or to unstable areas (both covering about 48% of the investigated areas). The latter are sometimes combined with geomorphological features such as scarps, isolated peaks, and ridges that are also responsible for possible site amplification. In addition, a susceptibility to local seismic amplification index has been introduced which highlights that more than 64% of the investigated area, along with a significant percentage of buildings, fall within the highest categories of susceptibility to local seismic amplification.

Mediterranean marginal basins recorded the Messinian salinity crisis (MSC) in various structural settings, including syn-rift, thrust-top, foredeep, and foreland basins. During the MSC, the Apennines were one of the mobile belts of the peri-Mediterranean chain. Starting from more hinterland areas, allochthonous units of both the northern and southern Apennines migrated toward the Adriatic foreland, developing allochthonous-top sedimentary basins. One of these basins, on top of the Molise allochthonous units (southern Apennines), recorded almost all of the main steps of the MSC. In a gypsum quarry district, the occurrence of conduits yielding flow-mobilized sediments, which cross-cut the Lower Evaporites, testifies to a fluid-migration event responsible for the formation of a brecciated mudgrade limestone buildup. This event can be connected with the Mediterranean drawdown responsible for the Messinian erosional surface (MES). The post-evaporitic marly succession that unconformably overlies the Lower Evaporites and the “Brecciated limestones” is characterized by the presence of Paratethyan molluscs and ostracods (Loxoconcha muelleri and Loxocorniculina djafarovi zones), and small mammals, among which is recorded the occurrence of Stephanomys debruijni. A disconformity within the post-evaporitic succession divides it into lower (p-ev1) and upper (p-ev2) Lago-Mare deposits. A further erosional surface separates the Messinian Lago-Mare sediments from fully marine lower Zanclean (MPl2 Zone) deposits. Whilst the unconformity separating the Lower Evaporites and the Lago-Mare deposits (although enhanced by a tectonic event) could be related to a late Messinian base level drop (MES1), as well as the disconformity between p-ev1 and p-ev2 (MES2), the younger angular unconformities affecting both the Lago-Mare deposits (p-ev2) and the fully marine Pliocene sediments might be related to two different phases of orogenic transport. Those events affected the Molise allochthonous units during their Late Miocene-Early Pliocene forelandward migration.

This paper concerns the reconstruction of the main stages of the long-term landscape evolution of the Molise portion of the central-southern Apennines along a transect divided into three sectors (SW, Central and NE). Analysis mainly focused on geomorphological, stratigraphical and structural data supported by chronological constraints, coming from an overall review of past literature and several studies carried out by the authors of the paper during the last 20 years. The results obtained allowed the elaboration of a conceptual model of the long-term evolution of the Molise sector of the central-southern Apennines. Starting from the Pliocene, the emersion of the Molise area occurred gradually from SW to NE, allowing a polycyclic landscape to evolve under the major controls first of compression then transtensional to extensional tectonics as well as climatic variations. Principal markers of the Quaternary geomorphological evolution of the Molise area are represented by the infill successions of the intermontane tectonic depressions located in its internal, SW sector and by four orders of palaeosurfaces that developed between the Early Pleistocene and the beginning of the Late Pleistocene across the region. These markers testify to the alternation of phases of substantial tectonic stability and uplift whose spatial-temporal distribution could be assessed along the investigated transect. Results highlight that the most important stages of landscape evolution occurred during the Early and Middle Pleistocene. At the beginning of the Late Pleistocene, the Molise sector of the Apennine chain had already reached its present setting and further landscape evolution occurred under the major control of climate and land-use.

A buried paleovalley system, up to 2km wide and exceeding 50m in relief, made up of multiple cross-cutting depressions incised into the Lower Pleistocene bedrock, is reported from the central Adriatic coastal plain at the mouth of Biferno River. Through a multi-proxy approach that included geomorphological, stratigraphic, sedimentological and paleontological (benthic foraminifers, ostracods and molluscs) investigations, the facies architecture of distinct, superposed valley fills is reconstructed and their relative chronology established along a transverse profile with extremely high data density (average borehole spacing 75m). Regional tectonic uplift appears as the major controlling factor of initial (Middle Pleistocene) river down-cutting and paleovalley formation. In contrast, glacio-eustatic fluctuations drove fluvial-system response over the last 120ky, when valley incision was primarily induced by the last glacial base-level lowering and climatic forcing. A fragmented record of coastal and shallow-marine deposits is available for the lower paleovalley fill, which is penetrated by a limited borehole dataset. Multiple erosion phases probably related to the post-MIS 5e sea-level fall are reconstructed from the upper paleovalley fill, where a buried fluvial terrace succession is identified a few tens of meters below the ground surface. The flat surfaces of two buried fluvial terraces suggest longer-term, stepped relative sea-level fall, and are correlated with fluvial incisions that took place possibly at the MIS 5/4 transition and at the MIS 3/2 transition, respectively. A laterally extensive gravel body developed on the valley floor during the Last Glacial Maximum. During the ensuing latest Pleistocene–early Holocene sea-level rise the Biferno paleovalley was transformed into an estuary. Upstream from the maximum shoreline ingression, the vertical succession of well-drained floodplain, poorly-drained floodplain, and swamp deposits evidences increasing marine influence in the estuary, in response to continuing sea-level rise. The interfluves were drowned around 8cal.ky BP, when brackish conditions developed in the study area. Decreasing marine influence in the uppermost 15m of the paleovalley fill suggests the onset of the modern delta: when the rate of sea-level rise was overwhelmed by sediment supply, delta progradation took place.

The results of palaeontological analyses carried out on foraminifers, molluscs and ostracods from a 15 m thick core (MBS3), drilled offshore in the Trigno River mouth area (northern sector of the Molise Adriatic coast), ca. 200 m from the present coastline, are reported.Four main lithostratigraphic units were recognised in the core. At the bottom, 1.8 in thick, barren gravels (unit A), are present. Grey clays (unit B), 1.5 m thick, containing freshwater and terrestrial molluscs, freshwater ostracods and reworked marine foraminifers and ostracods, overlay unit A. Brown silty clays (unit C), 2.7 m thick, containing marine foraminifers and ostracods, rare marine molluscs, and subordinate freshwater ostracods, follow. The core is closed up by brown sands (unit D), 9 m thick, recording the dominance of marine foraminifers, molluscs and ostracods. Chronological constraints for the studied sedimentary succession are based on AMS (Accelerator Mass Spectrometry) radiocarbon dating.The lower gravel unit A of the core MBS3 deposited in an alluvial environment. The sedimentological and palaeontological characters of unit B indicate marshy freshwater environments. Two AMS C dates of this unit gave ages of 19945 +/- 345 and 19165 +/- 195 yr cal BP, respectively The sedimentological and palaeontological characters of unit C indicate the development in the Trigno River mouth area of a bay or outer estuarine environment. Finally, as revealed by the deposition of unit D, about 8000-8200 yr BP a shoreface developed in the Trigno mouth area.

A basin-scale, integrated approach, including sedimentological, geomorphological and soil data, enables the reliable reconstruction of the infilling history of the southern Apenninic foredeep, with its subsequent inclusion in the wedge-top of the foreland basin system. An example is shown from the Molise-Apulian Apennines (Southern Italy), between Trigno and Fortore rivers, where the Pleistocene tectono-sedimentary evolution of the basin is framed into a sequence-stratigraphic scheme. Specifically, within the traditional subdivision into Quaternary marine (Qm) and Quaternary continental (Qc) depositional cycles, five third-order depositional sequences (Qm1, Qm2, Qc1, Qc2 and Qc3) are identified based on recognition of four major stratigraphic discontinuities. The lower sequence boundaries are represented by angular unconformities or abrupt facies shifts and are generally associated with distinctive pedological and geomorphological features. Three paleosols, observed at top of depositional sequences Qm2, Qc1 and Qc2, represent pedostratigraphic markers that can be tracked basinwide. The geomorphological response to major tectono-sedimentary events is marked by a series of paleosurfaces with erosional, depositional and complex characteristics. Detailed investigation of the relationships between stratigraphic architecture and development of unconformities, paleosols and paleosurfaces suggests that the four sequence boundaries were formed in response to four geomorphological phases/tectonic events which affected the basin during the Quaternary. The first three tectonic events (Lower-Middle Pleistocene), marking the lower boundaries of sequences Qm2, Qc1 and Qc2, respectively, are interpreted to be related to the tectonic regime that characterized the last phase of thrusting recorded in the Southern Apennines. In contrast, sequence Qc3 does not display evidence of thrust tectonics and accumulated as a result of a phase of regional uplift starting with the Middle Pleistocene.

Integrated sedimentological and micropalaeontological analyses of Montesecco Clays cropping out along the Molise Apennines foothills allow to reconstruct the depositional setting and major palaeoenvironmental changes within the Molise Periadriatic Basin (Apenninic foredeep) during the Late Pliocene and Early Pleistocene. Sedimentological and palaeocological data from four reference stratigraphic sections document an overall shallowing-upward tendency within Montesecco Clays, which is also confirmed by compositional data analysis of microfaunal assemblages. Lower Montesecco Clays (Ururi and Trigno sections) accumulated from the middle epibathyal/bathyal to lower circalittoral zone, while upper Montesecco Clays (Guglionesi and Colle Favaro-Petacciato sections) contain a microfauna indicative of an outer circalittoral to infralittoral environment. As documented by previous subsurface data, the palaeoecological analysis suggests increasing depths in the Molise Periadriatic Basin from NW to SE.

The active tectonic regime along the outer Northern Apennines (Padan–Adriatic area) is a matter of debate. We analyse the active tectonic regime by systematically inverting earthquake focal mechanisms in terms of their driving stress field, comparing two different stress inversion methods. Earthquakes within the area often deviate from Andersonian conditions, being characterized by reverse or transpressional slip on high-angle faults even if the regime is almost purely thrust faulting (e.g. Reggio Emilia 1996 and Faenza 2000 earthquakes). We analyse the stress conditions at faulting for the Reggio Emilia and Faenza earthquakes in order to infer the stress magnitudes and the possible role of fluid pressures.